• Preheat the oven to 350°F (180°C).

Prepare the caramel.

• Place the sugar and water in a medium heavy bottomed saucepan over medium-high heat, and cook without stirring until sugar dissolves and gets a caramel color.
• Remove the pan from the heat and add the butter. Pour the caramel into a 8 inch (20cm) pan. If you use a springform pan place the pan over a tray in case some caramel leaks out.
• Arrange the plum wedges in the caramel and set aside until you prepare the batter.

Prepare the cake batter.

• In a medium bowl whisk the flour with baking powder, cinnamon and salt. Set aside until ready to use.
• In a large mixing bowl rub sugar and lemon zest together to release oil. Add butter and mix until creamy. Incorporate eggs one at a time. Add sour cream and vanilla extract and mix to combine.
• With the mixer on low gradually incorporate the flour mixture.
• Pour batter over the plum wedges on the pan.
• Bake for about 40-50 minutes until a toothpick inserted into the center comes out clean.
• Let cool for 10 minutes, and then invert onto a serving platter.
• Serve as is or with a good dollop of ice cream or cream on top.